Question 121842 in Redis Question posted in
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Reset scores of Redis sorted set after zremrangebyscore

I’m using Redis sorted set to keep some values in order. for example:

score | data
0     |  a
1     |  b
2     |  c
3     |  d

In some situations of my app, I have to remove some of the entries. for example, I delete scores 1 and 2 members:

score | data
0     |  a
3     |  d

I want to change the above to:

score | data
0     |  a
1     |  d

How can I do this?

please help, thanks in advance.

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3

Answers


  1. Chosen as BEST ANSWER
    0

    After searching and hard work, I found the solution.

    You can use Lua script and EVAL command:

    EVAL 
"
redis.call('ZREMRANGEBYSCORE', KEYS[1], KEYS[2], KEYS[2]);
local otherMembers = redis.call('ZRANGEBYSCORE', KEYS[1], KEYS[2], 1/0);
for k, v in ipairs(otherMembers) do
redis.call('ZINCRBY', KEYS[1], -1], v);
"
2 key index;

  2. 0

    I think it’s not possible to use a sorted list in Redis like an indexed array.

    If you want to have a sorted list with a sequential score you should take care of it yourself so after every delete, you can overwrite your sorted list with new scores.

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  3. 0

    It seems that you don’t need the score, instead, you need the rank.

    You can keep a monotonically increasing counter, which starting from 0, and each time when you need to add an element to the set, call incr on the counter to get a score, and insert the element into the set. So that, each new element will always has the largest score, i.e. new element will rank lower than old elements.

    127.0.0.1:6379> incr counter
(integer) 1
127.0.0.1:6379> zadd set 1 a
(integer) 1
127.0.0.1:6379> incr counter
(integer) 2
127.0.0.1:6379> zadd set 2 b
(integer) 1
127.0.0.1:6379> incr counter
(integer) 3
127.0.0.1:6379> zadd set 3 c
(integer) 1
127.0.0.1:6379> incr counter
(integer) 4
127.0.0.1:6379> zadd set 4 d

    You can use ZREMRANGEBYRANK to remove elements, and ZRANK to get the rank of each element (the rank always start from 0).

    127.0.0.1:6379> zremrangebyrank set 1 2
(integer) 2                              <------- remove b and c
127.0.0.1:6379> zrank set a
(integer) 0
127.0.0.1:6379> zrank set d
(integer) 1
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